Such drivable devices for compacting a soil layer structure are known from the prior art. For example, there are machine driven rollers, and in particular road rollers, by which a soil layer structure, and in particular an asphalt road including its substrate, can be compacted. For this purpose, the drivable devices and also the above-mentioned road roller have a vibration means or device, via which load pulses which compact the soil layer structure can be introduced into the surface of the soil layer structure.
The drivable device moves in multiple work steps over the soil layer structure to be compacted, a further compaction up to a maximum compaction being achieved upon each passage. After achieving the maximum compaction, further compaction of the soil layer structure is no longer necessary or is even counterproductive, because it results in renewed loosening of the compacted soil layer structure and excess strain of the compaction device. For this reason, it is important to detect the degree of compaction of the soil layer structure continuously or at specific intervals.
However, it is problematic in this case that because of the structure of the soil composed of different layers, precise detection of the moduli of elasticity of the respective layers, i.e., the layer moduli of elasticity, is only imprecisely possible, since the moduli of elasticity of the individual layers, in particular unbound layers, mutually influence one another.
A method using the so-called “falling weight deflectometer” (FWD) is known from the prior art, in which a relatively precise detection of a layer modulus of elasticity is possible by ascertaining a depression trough caused by a load pulse via an established number of detection devices. In particular, in the case of the evaluation of the carrying capacity of existing asphalt roads, the carrying capacity studies using the FWD are increasingly gaining significance. Using the FWD, a load pulse is applied to the road surface using a falling mass, which serves to simulate a wheel rollover. The briefly occurring vertical deformation of the surface of the soil layer structure is recorded in the load center and remotely at eight predefined distances from the load center.
The stiffness of the entire road structure is ascertained via the measured depressions of the depression trough. The influence of the deeper layers on the measured depressions increases with increasing distance from the load introduction point. This means that the depression at the load introduction point is a function of the carrying capacity of the entire layer structure, while the depression at the most remote pickup is essentially determined by the carrying capacity of the substrate or deeper layers. The calculation of the stiffnesses or the layer moduli of elasticity is then performed based on the theory of the elastic half-space and a multilayer model (e.g., a 2-layer or 3-layer model) according to Boussinesq/Odemark.
The modulus of stiffness at the load introduction point results in the so-called equivalent modulus, i.e., the modulus of elasticity of the entire soil layer structure under the influence of all layers. At the far remote measuring point, the so-called bedding modulus, the modulus of elasticity of the substrate, is ascertained. The moduli of elasticity of the individual layers are then ascertained by means of back calculation from the measured depression troughs or moduli of elasticity of the roadway. The layer thicknesses of the bound and unbound carrier layers are incorporated in the calculation.
However, this method has the disadvantage that the ascertainment of the layer moduli of elasticity using the FWD is very time-consuming and no further work can be performed on the soil layer structures during the measurement. The values obtained by the FWD are also only available to a soil compaction device, and in particular a road roller, after a time delay, so that a compaction-controlled method or the compaction-controlled soil compaction is only possible with difficulty.